"Annet Mahendru has been a revelation as Nina, bringing the character to life with a rich and subtle depth that keeps you guessing as to what's really percolating under the surface," executive producers Joe Weisberg and Joel Fields said in a statement. "And Alison Wright's portrayal of Martha is heartbreakingly real at every turn. We are thrilled to add them to our outstanding company of actors."

Susan Misner, who plays Sandra Beeman, the wife of Stan, has also been bumped up to series regular.